1. Field of the Invention
The present invention relates to a method of forming a preserve layer. More particularly, the present invention relates to a method of fabricating a preserve layer of a reflection micro-LCD.
2. Description of the Related Art
Reflection micro-LCD is operated by applying voltage to a top metallic layer, which is used for controlling a circuit, in order to generate an electrical field for governing the arrangement of liquid crystals. When lights transmit through liquid crystals to the top metallic layer, the top metallic layer reflects the lights to return the lights through the liquid crystals. Since different arrangements of the liquid crystals represent different optical properties, different pictures can be shown on a display.
In order to prevent moisture and scratches from damaging the surface of the top metallic layer, a preserve layer is formed to protect the top metallic layer. However, the structure and the thickness combination of the preserve layer directly affect the reflectivity of the top metallic layer. Thus, the formation of the preserve layer is a decisive step during the fabrication process of the reflection micro-LCD.
FIGS. 1A through 1B are schematic, cross-sectional views showing a conventional method of fabricating a preserve layer.
In FIG. 1A, a dielectric layer 102 is formed on a substrate 100. An adhesion layer 104 and a metallic layer 106 are formed in sequence over the substrate 100. Portions of the top metallic layer 106, the adhesion layer 104, and the dielectric layer 102 are removed to form a trench 108. It is necessary to form the trench 108 completely through the top metallic layer 106, in order to separate the metallic layer 106 into different regions.
In FIG. 1B, a conformal oxide layer 110 is formed over the substrate 100. The thickness of the oxide layer 110 is 5000 angstroms. A nitride layer 112 having a thickness of 7000 angstroms is formed on the oxide layer 110 to fill the trench 108. The oxide layer 110 and the nitride layer 112 together form a preserve layer 114. However, since the preserve layer 114 is particularly thick, the transmissivity of the preserve layer 114 is reduced. Consequently, the reflectivity of the top metallic layer 106 is significantly decreased.
In addition, the conventional method forms the preserve layer 104 with poor planarization. When light transmits through the preserve layer 104, the transmissivity of the preserve layer 114 is reduced due to poor planarization of the preserve layer 114. The reflectivity of the top metallic layer 106 is decreased to 30%. Thus, it is difficult to form a top metallic layer 106 with a high reflectivity.